Is it a stock clutch or something grippier? Grippy cluthes "shutter" into position by their nature. This is the price you pay for greater power holding capability.
The petal sticking down is not related to the actual clutch. Sometimes the clutch master cylinder goes bad (dunno if that's the right term). It's a very common problem on those years.
The symptom of clutch failure is the car acting like it's not in gear once it's in gear. Specifically as you add more power. The test is to engauge the clutch at low RPMS and then accelerate through the power band. If the car suddenly feels like it just came out of gear at some point, then you know the clutch is starting to go. Another symptom is a lack of "meat" at the grip point. It often gives a feeling like you cannot tell where the actual connection point is. It's soft and vague and higher on the petal than it used to be.
2015 STi: Still Stock
04 STi, 04 WRX: SOLD